feat: add code transformer to <Demo> component

packages/docusaurus-theme/src/components/demo/code_transformer.ts

@@ -0,0 +1,36 @@
+const IMPORT_REGEX = /^import [^'"]* from ['"]([^.'"\n ][^'"\n ]*)['"];?/gm;
+const DEFAULT_EXPORT_REGEX = /export default /;
+const COMPONENT_ONLY_REGEX = /^\(?</;
+
+/**
+ * Transforms input JS/TS source code to a react-live compatible syntax.
+ * react-live uses the surcase library to transform input source code into
+ * browser-readable JavaScript.
+ *
+ * While surcase does support CommonJS and ESM import/export statements,
+ * it's not trivial to expose our internal React and EUI exports through it
+ * and because we already control the execution scope of the interactive demos
+ * it isn't really necessary to implement a smart `require()` replacement.
+ *
+ * Returning an IIFE is necessary when the source code is more than just
+ * a JSX component definition (e.g. it contains a variable definition
+ * or `export default` statement).
+ *
+ * @see {@link https://github.com/alangpierce/sucrase}
+ * @see {@link https://github.com/FormidableLabs/react-live/blob/master/packages/react-live/src/utils/transpile/index.ts}
+ */
+export const demoCodeTransformer = (code: string) => {
+  // Remove ESM imports
+  code = code.replace(IMPORT_REGEX, '');
+
+  // Handle ESM default exports
+  code = code.replace(DEFAULT_EXPORT_REGEX, 'return ');
+
+  // If the demo is JSX only return as-is
+  if (COMPONENT_ONLY_REGEX.test(code)) {
+    return code;
+  }
+
+  // If the demo is more than just JSX wrap in an immediately invoked function expression
+  return `(() => { ${code} })()`;
+}

packages/docusaurus-theme/src/components/demo/demo.tsx

@@ -1,15 +1,26 @@
-import { Children, PropsWithChildren, useCallback, useState } from 'react';
+import {
+  Children,
+  PropsWithChildren,
+  useCallback,
+  useMemo,
+  useState,
+} from 'react';
 import { isElement } from 'react-is';
 import { LiveProvider } from 'react-live';
 import { themes as prismThemes } from 'prism-react-renderer';
-import { useEuiMemoizedStyles, copyToClipboard, UseEuiTheme } from '@elastic/eui';
+import {
+  useEuiMemoizedStyles,
+  copyToClipboard,
+  UseEuiTheme,
+} from '@elastic/eui';
 import { css } from '@emotion/react';
 import { DemoContext, DemoContextObject } from './context';
 import { DemoEditor } from './editor';
 import { DemoPreview } from './preview';
 import { DemoSource } from './source';
-import { demoScope } from './scope';
+import { demoDefaultScope } from './scope';
 import { DemoActionsBar } from './actions_bar';
+import { demoCodeTransformer } from './code_transformer';
 
 export interface DemoSourceMeta {
   code: string;
@@ -18,11 +29,19 @@ export interface DemoSourceMeta {
 }
 
 export interface DemoProps extends PropsWithChildren {
+  /**
+   * Whether the source code editor is open by default
+   */
   isSourceOpen?: boolean;
+  /**
+   * Allows to extend the default scope of the rendered demo and pass additional
+   * properties available within the demo.
+   *
+   * The default scope exposes all React and EUI exports.
+   */
+  scope?: Record<string, unknown>;
 }
 
-const transformCode = (code: string) => code;
-
 const getDemoStyles = (euiTheme: UseEuiTheme) => ({
   demo: css`
     --docs-demo-border-color: ${euiTheme.euiTheme.colors.lightShade};
@@ -36,6 +55,7 @@ const getDemoStyles = (euiTheme: UseEuiTheme) => ({
 
 export const Demo = ({
   children,
+  scope,
   isSourceOpen: _isSourceOpen = true
 }: DemoProps) => {
   const styles = useEuiMemoizedStyles(getDemoStyles);
@@ -46,9 +66,17 @@ export const Demo = ({
   // liveProviderKey restarts the demo to its initial state
   const [liveProviderKey, setLiveProviderKey] = useState<number>(0);
 
-  const addSource = useCallback<DemoContextObject['addSource']>((source: DemoSourceMeta) => {
-    setSources((sources) => ([...sources, source]));
-  }, []);
+  const finalScope = useMemo(() => ({
+    ...demoDefaultScope,
+    ...scope,
+  }), [scope]);
+
+  const addSource = useCallback<DemoContextObject['addSource']>(
+    (source: DemoSourceMeta) => {
+      setSources((sources) => ([...sources, source]));
+    },
+    [],
+  );
 
   const onClickCopyToClipboard = useCallback(() => {
     copyToClipboard(activeSource?.code || '');
@@ -69,9 +97,9 @@ export const Demo = ({
         <LiveProvider
           key={liveProviderKey}
           code={activeSource?.code || ''}
-          transformCode={transformCode}
+          transformCode={demoCodeTransformer}
           theme={prismThemes.dracula}
-          scope={demoScope}
+          scope={finalScope}
         >
           <DemoPreview />
           <DemoActionsBar

packages/docusaurus-theme/src/components/demo/editor/editor.tsx

@@ -17,6 +17,8 @@ const getEditorStyles = () => ({
 
     & .prism-code {
       border-radius: 0 0 calc(var(--docs-demo-border-radius) - 1px) calc(var(--docs-demo-border-radius) - 1px);
+      max-height: 450px;
+      overflow: auto;
     }
   `,
   error: css`

packages/docusaurus-theme/src/components/demo/preview/preview.tsx

@@ -1,5 +1,5 @@
 import { css } from '@emotion/react';
-import { LiveError, LivePreview } from 'react-live';
+import { LivePreview } from 'react-live';
 import BrowserOnly from '@docusaurus/BrowserOnly';
 import ErrorBoundary from '@docusaurus/ErrorBoundary';
 import { ErrorBoundaryErrorMessageFallback } from '@docusaurus/theme-common';
@@ -30,9 +30,9 @@ export const DemoPreview = () => {
       {() => (
         <>
           <ErrorBoundary fallback={(params: any) => <ErrorBoundaryErrorMessageFallback {...params} />}>
-            <EuiFlexGroup css={styles.previewWrapper} alignItems="center" justifyContent="center">
+            <div css={styles.previewWrapper}>
               <LivePreview />
-            </EuiFlexGroup>
+            </div>
           </ErrorBoundary>
         </>
       )}

packages/docusaurus-theme/src/components/demo/scope.ts

@@ -1,8 +1,11 @@
 import React from 'react';
 import * as EUI from '@elastic/eui';
 
-export const demoScope: Record<string, unknown> = {
+export const demoDefaultScope: Record<string, unknown> = {
+  // React
   React,
   ...React,
+
+  // EUI exports
   ...EUI,
 };